Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 191040
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
640 AM EDT Wed Jul 19 2017

.NEAR TERM...(Today through Tonight)
Issued at 325 AM EDT Wed Jul 19 2017

...Another generally nice day today...

High impact weather potential...none.

Cold front making slow progress across northern lower and far
eastern upper MI. Appears to be thru APN but not quite HTL.
Convective remnants in the vicinity of this front (both ahead and
behind) have generally been decaying, though a cluster of showers
near MBL is fighting off that trend. A narrow instability plume
overhead is weakening with time, aiding the decay process.
Leftover precip chances are the initial concern for today, along
with post-frontal low clouds. Showers might return tonight as
return flow ramps up again to our west.

Will take another 4-6 hrs for lingering showers to clear the
forecast area. Anticipate little if any precip threat after 14-15z,
as somewhat cooler/drier air moves in, and as 500mb heights start to
rise ahead of a wave exiting the northern plains. Just the tiniest
sliver of MlCape is progged in the far se, where moisture pools a
bit ahead of the Lake Huron lake breeze. Do not think we can take
advantage of that.

Area of post-frontal low clouds covers much (but not all) of eastern
Superior/eastern upper MI/northern Lake MI, and is making some
inroads into far northern lower. Drier air will make a somewhat
faster intrusion into eastern upper MI, and anticipate them
clearing our relatively quickly this morning. Cloud deck will be
widespread enough in northern lower MI to resist mixing out until
late morning or even midday. The high July sun angle will win out
eventually.

Max temps a touch cooler than yesterday, upper 70s to mid 80s.

Environment upstream late today/this evening is highly charged for
organized MCS development. Highly unstable airmass from SD to
northern IL, with 0-6km bulk shear values above 60kt in a broad area
along the north edge of said airmass. This MCS is likely to
eventually charge ese-ward, toward southern Lake MI overnight.
There are some models (including the ECMWF) that charge the MCS
due east into lower MI, but it should be pretty strongly compelled
to follow the surface front and edge of the instability plume
further south. So the primary MCS is unlikely to have a
substantial impact here, though will bring some showers late (no
thunder) to TVC/CAD and points west.

However, the Nam in particular is wont to develop some showers
very late tonight over northern MI. The environment has zero
Cape, but with a weak shortwave moving in from the wnw and
associated mid-level height falls, it conjures enough moisture for
some rain. This looks like a stretch from here, and will carry
only a slight chance of showers for parts of eastern upper MI late
tonight.

Min temps also a touch cooler, mid 50s to around 60f.

&&

.SHORT TERM...(Thursday through Friday)
Issued at 325 AM EDT Wed Jul 19 2017

...Occasional chances for showers and thunderstorms...

High Impact Weather Potential: Chance of thunder Thursday and again
Friday afternoon.

Pattern Forecast: Well-advertised progressive zonal flow across the
northern states into southern Canada will feature little change for
the remainder of the week. Several mid level perturbations rotating
into the Pac NW will be the main driver to our local weather as the
energy quickly races eastward, pushing across the Great Lakes and
Ohio Valley at various points Thursday - Friday, and again this
weekend.

Primary Forecast Concerns/Challenges: Temporal and spatial
resolution of any precipitation chances/MCS potential to end the
work week as guidance continues to struggle in resolving what are
ultimately mesoscale features.

Details: As was alluded to above, guidance is continuing to have an
awfully tough time consistently resolving mesoscale features and
their boundary layer interaction late this week into the upcoming
weekend as several lobes of energy quickly race from the northern
Rockies eastward across the central/northern Plains into the Great
Lakes. Thus, while there remains high confidence in occasionally wet
weather through Sunday, lower than desired confidence prevails in
the temporal/spatial details.

Beyond a break in the potential action Wednesday evening, the next
wave begins to take shape across the northern Plains as the low
level jet responds to an upper level speed max traversing the upper
MS Valley. Current indications point toward a decaying MCS diving
southeastward across Wisconsin toward southern Lake Michigan late
Wednesday night-Thursday morning. While there remain some outlier
guidance members that try to scream it across areas south of M-72,
still believe the greatest threat for this will remain south...
colocated with low level jet placement, deeper moisture, and
greatest instability gradient. However, will feature chance PoPs
locally through the day Thursday, most widespread in the morning
becoming confined toward northeast Lower during the afternoon,
perhaps aided by afternoon lake breeze development. SPC broadly
highlights the entire CWA in a Day 2 Marginal Risk (despite
unfavorable jet structure aloft over northern Michigan) warranted by
increasing diurnal instability with MLCAPEs progged near 1,000 J/kg,
~45 kts of bulk shear, and a mid level shortwave traversing the
region through this time. A similar story for Friday as northern
Michigan lies on the northern periphery of a warm, humid airmass
with another threat for showers and storms, mainly during the late
afternoon-evening (but a better threat again to the south as another
MCS looks possible in similar locales as Wednesday night). Friday`s
threat once again tied to subtle nuances that have plenty of time to
waffle back and forth in the next 48 hours.

Thursday high temperatures progged in the upper 70s north to the
lower 80s elsewhere. Even warmer and more humid Friday ranging from
the low to middle 80s. Would expect some refinement to temps over
the next 24-48 hours as convective trends become more clear, which
may have an impact on high temperatures.

.LONG TERM...(Friday night through Tuesday)
Issued at 325 AM EDT Wed Jul 19 2017

High impact weather potential: Additional scattered thunderstorms
possible Saturday and Sunday.

Little change in the overall large scale pattern through Sunday as
several additional and slightly more impressive pieces of energy
converge on the midsection of the country. Wet/stormy weather remains
possible Saturday and Sunday, although would expect some dry time
mixed in as well. What looked like a clear cut stretch of precip-
free weather early next week has started to to fall by the wayside
within the last 24 hours as several ensemble guidance members
attempt to linger showers Monday as ridging builds across the East
Coast allowing upstream troughing to deepen and spin across the
northern Great Lakes. Gut feeling is that the majority of early next
week still ends up mainly dry (especially beyond Monday) as high
pressure settles in with decidedly cooler temps falling back below
normal.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 640 AM EDT Wed Jul 19 2017

Cigs improving later this morning.

IFR to low-end MVFR cigs have migrated into northern lower MI,
behind a departing cold front. The low clouds will erode and mix
out this morning, with mainly clear skies for much of the
afternoon and early evening. High clouds will thicken later
tonight, and it`s not out of the question for a shower to approach
MBL/TVC toward 12Z.

Light nw winds today, nearly calm winds tonight.

&&

.MARINE...
Issued at 325 AM EDT Wed Jul 19 2017

Light nw winds today behind a passing cold front. These may be a
touch gusty, in particular going by Presque Isle Lt on Lake Huron.
Advisories are not warranted. Winds will tend more southerly on
Thursday, though light enough for onshore lake breezes to become
prevalent later in the day.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...NONE.
LM...NONE.
LS...NONE.
&&

$$

NEAR TERM...JZ
SHORT TERM...MG
LONG TERM...MG
AVIATION...JZ
MARINE...JZ



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